1. Field of the Invention
This invention concerns a process for curing a tire using a curing bladder.
2. Description of the Prior Art
Pneumatic rubber tires for use in vehicles have heretofore been produced by molding and curing green tires in a molding press, in which the green tires are pressed outwardly to the surface of a die by an internal fluidexpanded bladder. In this method, the green tire is molded and vulcanized conforming the surface of an external die that determines the tred pattern and the side wall structure of the tire.
Heretofore, organic rubber, particularly, butyl rubber has been used as the composition of the curing bladder for use in the molding and vulcanization of rubber tire products. However, a curing bladder composed of an organic rubber such as butyl rubber has poor releasability from the inner surface of the tire and tends to be bent upon detaching the tire, thus causing failure upon tire molding in the die. Further, the surface of the bladder is roughened by the abrasion and possibly adheres to the inner surface of the tire after the curing of the tire or in the course of bladder shrinkage during the tire curing cycle. In addition, gas bubbles are confined between the bladder and the tire surface to render the heat transfer insufficient, thereby promoting the defects in the vulcanization of the tire.
In view of the above, a releasing agent such as one composed of a silicon emulsion has been required in the conventional curing bladder in order to improve the lubricating nature to the inner surface of the tire. However, application of the releasing agent to the inner surface of the tire provides disadvantages in that the number of steps is increased in view of the manufacturing process and intermediate stocks are increased, as well as the releasing agent gives undesired effect upon tire molding and vulcanization, thereby often resulting in failed products.
As a countermeasure for overcoming such problems, there has been attempted a method of modifying the surface of the organic rubber constituting the curing bladder with silicone and the use of methyl hydrogen silane or dimethyl hydrogen silane (Japanese Patent Application Laid-Open No. 57-111394) or the use of hydroxyl silane (Japanese Patent Application Laid-Open Nos. 57-111393 and 119992).
However, in the conventional methods of applying surface modifications to the organic rubber with silicone as described above, although the releasability between the surface of the bladder and the inner surface of the tire can be improved and the tire can be molded and vulcanized without using the releasing agent, the durability of the surface of the bladder is extremely worsened, making it unsuitable for practical use. Therefore, it has been desirable to develop a curing bladder having excellent physical properties such as mechanical strength, heat resistance and hydrothermal resistance, as well as excellent releasability.